The disclosure relates to a linear motion device having an anti-twist safeguard, comprising an elongate anti-friction lining.
EP 0 767 526 B1 has disclosed a linear motion device in the form of an electric cylinder. According to FIG. 3 of EP 0 767 526 B1, the linear motion device 10 comprises a housing 12 and an extension arm 30, which projects from the housing. In this arrangement, the housing and the extension arm are constructed in the form of a hollow cylinder, with the extension arm being accommodated in the through bore 11 of the housing and being supported in the housing in such a way that it can move along a longitudinal axis.
The extension arm can be set in motion by means of a screw drive. The screw drive comprises a threaded spindle 24, which is supported in such a way that it can rotate relative to the longitudinal axis and is provided on the outer circumferential surface thereof with helical thread flights 22. Engaging in the thread flights is a matching threaded nut 28 which, in the case under consideration, is formed integrally with the extension arm. However, the prior art also includes electric cylinders in which the threaded nut is constructed in the form of a separate nut with recirculating spherical rolling elements, the nut being connected securely to one end of the extension arm. Rotary motion can be imparted to the threaded spindle by an electric motor 20 which, in the case under consideration, is coupled directly to the threaded spindle. However, it is also possible for a transmission, e.g. a belt or gear-type transmission, to be provided between the electric motor and the threaded spindle.
An anti-twist safeguard is furthermore provided, supporting the torque which the electric motor imposes on the threaded spindle and thus preventing the extension arm from being twisted relative to the longitudinal axis with respect to the housing. For this purpose, the extension arm is equipped substantially over the entire length thereof with splines. The housing, for its part, engages positively, by means of part 36, in the splines.
Other cross-sectional shapes for the extension arm that deviate from the circular shape are also known as substitutes for the splines. In the case of the extension arm in FR 2587690 A1, for example, three flats are provided on an initially circular hollow tube.
The disadvantage of the anti-twist safeguard according to EP 0 767 526 B1 lies in the complex production of the many grooves of the splines. However, the splines have the advantage that there is a very large engagement surface overall. Moreover, this surface is aligned substantially perpendicular to the acting forces. Wear is correspondingly low. The extension arm in FR 2587690 A1, in contrast, is significantly easier to produce. However, wear minimization would require the provision of running rollers supported in rolling contact bearings to provide the positive engagement between the housing and the extension arm. This, in turn, is very complex.
It is the object of the disclosure to specify an anti-twist safeguard which is easy to produce and is furthermore subject to little wear.